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It is tempting to point to physiological fatigue mechanisms such as muscle cell depolarization that are in play in maximal efforts of 45 to 150 seconds. Muscles function somewhat like electric batteries, which require a strong difference in polarity to work at full power. During very high-intensity exercise, the muscles lose much of their polarity, just like a battery that’s running our of “juice,” and this causes a loss of muscle contractility and performance. However, research suggests that muscle cell depolarization cannot alone account for the loss or performance that occurs in sustained high-intensity efforts.

So what else is going on? Samuele Marcora believes that fatigue occurring in all maximal efforts lasting longer than half a minute or so is voluntary. The discomfort associated with the effort of sustaining a very high intensity of muscle work output becomes so great that the athlete essentially gives up. If this idea is new to you, you’re almost certain to receive it skeptically. Since I don’t want to get bogged down in defending it here, I will address your skepticism by referring you to my interview with Marcora.

What I would like to suggest here is that the performance threshold that runners encounter between maximal efforts of 45 and 150 seconds is associated with the activation of perceived effort as a cause of fatigue. In a 200-meter sprint, runners reach their maximal velocity at around 60 meters and start to slow down at around 150 meters. Thus, fatigue does manifest even in 20-second maximal efforts. But Marcora believes that fatigue in such short efforts is in fact caused by physiological factors, as everyone else believes. While there is obviously a very high perception of effort in a 200-meter sprint, this suffering does not trigger a conscious decision to slow down because the athlete knows it’s going to be over with soon enough.

When the races get longer, however, the psychological challenge exceeds the physiological challenge. And at some point, perception of effort, or psychological suffering, causes the runner to voluntarily restrain himself before there is actually any physiological necessity to slow down. That is the cause of the performance threshold that falls between 400 and 800 meters.

Do I have proof that this is so? Not direct proof. But an interesting 2009 study by researchers at the University of Essex in the United Kingdom provides oblique support for my conjecture. Nine subjects were asked to pedal absolutely as hard as they could on stationary bikes for 5 seconds, 15 seconds, 30 seconds, and 45 seconds. They were instructed not to worry about being unable to sustain maximum power in the longer efforts. The idea was to start each effort at absolute maximum intensity and then hang on as best they could.

That’s not what happened, though. Power data revealed that the subjects started the 45-second maximal effort at a slightly lower intensity than they started the shorter sprints. They couldn’t help themselves. Perceived effort data revealed that the subjects were not suffering as much 15 seconds into the 45-second effort as they were 15 seconds into the 30-second effort and at the end of the 15-second effort. This is what you would expect given that the subjects disobeyed instructions and restrained themselves slightly at the beginning of the 45-second effort, but it’s most certainly not what would have happened if the subjects had obeyed instructions. In that case they would have been suffering just as much at the 15-second mark of the 45-second sprint as they were at the 15-second mark of the 30- and 15-second sprints, with the consequence that they would have been suffering a lot more at the end of the 45-second sprint.

I believe that, probably based on past exercise experience, the subjects anticipated that they would reach an intolerable level of suffering if they truly went all-out for 45 seconds, so they paced themselves to avoid intolerable suffering and thus self-limited their performance.

They chickened out, as Marcora believes we all do in races longer than 400 meters.